Photos: ESA scientists discover ancient riverbed on Mars

European Space Agency (ESA) planetary geologists say they have discovered evidence of an ancient river bed on Mars supporting the theory that water once flowed on the Martian surface.

On Thursday, the agency released high-resolution images of parts of the "Reull Vallis region of Mars" which show a gigantic 932-mile-long (1500 kilometer) riverbed running from the Promethei Terra Highlands to the Hellas.

The images were snapped by ESA's Mars Express spacecraft cameras last year but were released for the first time on Thursday. The riverbed is believed to be the remains of a river that flowed on the surface of Mars billions of years ago.

ESA planetary scientists are deeply impressed by the size of the river. The images from ESA's Mars Express spacecraft show the riverbed widening to about 4.3 miles (7 kilometers) and 984 feet (300 meters) deep. The images also show several tributaries that feed the "gigantic" river much like on planet Earth.

According to ESA scientists, the river flowed about 3.5 to 1.8 billion years ago during an era of Mars' geological history called the Hesperian period. The Hesperian period was followed by the Amazonian. Mars geologists believe that during the Amazonian era, Reull Vallis was invaded by a glacier which brought debris and ice to the valley.

Reull Vallis

ESA

Planetary scientists attempting to interpret the features they observe in the Martian Reull Vallis terrain say it appears the Martian surface experienced geological processes similar to Earth's. Based on this insight, scientists say the dominant physical features on Reull Vallis are what would be expected of any glacial valley on Earth.

Topographic view of Reull Vallis

ESA

The images show the Promethei Terra Highland mountains rising "around 8,202 feet (2500 meters) above the surrounding flat plains." The geological formations and features are strikingly similar to those found on Earth's landscape, ESA scientists note. The region has features that bear striking resemblance to the "morphology found in regions on Earth affected by glaciation," ESA explains, although there are other formations in the region that are relatively unfamiliar.

3D view of Reull Vallis

ESA

The glacier that invaded Reull Vallis during the Amazonian era is believed to explain the peculiar features observable in the second perspective view below. According to ESA, planetary scientists think "the circular step-like structures on the inner walls of the sediment-filled crater in the foreground of the second perspective view may represent former high water or glacial levels, before ice and water sublimated or evaporated away in stages at various times.”

First perspective view of Reull Vallis

ESA

Second perspective view of Reull Vallis on Mars

ESA

ESA planetary scientists say the craters in the image were caused by meteors impacting the valley's surface. Scientists believe the craters in the region may be full of ice water.

Science Recorder notes, however, that some scientists have suggested that the channel is not the result of a single river but a series of rivers over geological time span. Others have even suggested that the riverbed was not formed by flowing water but by lava flows.